Bibliothek

X
feed icon rss

Ihre E-Mail wurde erfolgreich gesendet. Bitte prüfen Sie Ihren Maileingang.

Leider ist ein Fehler beim E-Mail-Versand aufgetreten. Bitte versuchen Sie es erneut.

Vorgang fortführen?

Exportieren
Filter
  • 2005-2009  (3)
  • 1995-1999  (122)
  • 1980-1984  (107)
  • 1
    Digitale Medien
    Digitale Medien
    Steady state model for polymer light-emitting electrochemical cells (1997)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 81 (1997), S. 2869-2880 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: A model is presented for the steady state operation of polymer light-emitting electrochemical cells (LECs). An LEC consists of a luminescent and ionically conducting polymer, with an ionic salt added to provide ions necessary for p-type and n-type doping, sandwiched between two electrodes. Upon applying a sufficiently large voltage bias, the ions are spatially separated forming an electrical junction. Electrons injected from the n-type side of the junction recombine with holes injected from the p-type side of the junction emitting light. We first describe the LEC at zero bias in which electric fields may occur in charge double layers near the contacts but in which there is a charge neutral, field free region in the device center which has an equal density of anions and cations and essentially no electrons or holes. A threshold voltage for junction formation is found, which depends on the polymer energy gap, the dissociation free energy of the salt, and the added salt density. It is generally somewhat smaller than the polymer energy gap. Below threshold, an applied bias changes the electric fields in the double charge layers near the contacts but the device center remains field free and essentially no current flows. Above threshold, the ions become spatially separated, a junction forms, and current begins to flow. Part of the applied voltage, above threshold, falls in the contact region and is necessary to establish the junction by electrochemical doping and part of the applied voltage falls across the junction. We describe the structure of the junction, which is quite different from that of a conventional p-n junction, including the spatial profiles of the electrons, holes, and ions, and the electrostatic potential. We discuss the current-voltage and capacitance-voltage characteristics of the LECs and show how they depend on the material parameters. © 1997 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.363966
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
    Volltext
  • 2
    Digitale Medien
    Digitale Medien
    Resonant tunneling in (001)- and (111)-oriented III–V double-barrier heterostructures under transverse and longitudinal stresses (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 7763-7769 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Calculations of the effects of external stress on the current–voltage characteristics of double-barrier (001)- and (111)-oriented resonant tunneling devices are presented. Crystal strains arising from the application of external pressure and, in pseudomorphic structures, lattice mismatch cause shifts in the conduction and valence bands of the well and barrier layers with respect to the unstrained alignment. For certain stress orientations piezoelectric effects give rise to internal electric fields parallel to the current direction. The combined piezoelectric and band-structure effects modulate the transmission resonances which control the shape of the current versus voltage characteristics of the structures. © 1996 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.362381
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
    Volltext
  • 3
    Digitale Medien
    Digitale Medien
    Nondegenerate continuum model for polymer light-emitting diodes (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 78 (1995), S. 4244-4252 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We present a device model to describe polymer light-emitting diodes (PLEDs) under bias conditions for which strong electrical injection does not occur (i.e., reverse, zero, and weak forward bias). The model is useful to interpret: capacitance–voltage measurements, which probe the charged trap density in the PLEDs; electroabsorption measurements on PLEDs, which probe the built-in electric field in the device; and internal photoemission measurements, which probe the effective Schottky barriers at the contacts of the PLED. The device model is based on the low-density nondegenerate continuum model for the electronic structure of polymers. Polarons and bipolarons are the principal charged excitations in this model. Polarons are singly charged excitations which play the primary role in charge injection and in experiments such as internal photoemission which probe single particle interface properties. Bipolarons are doubly charged excitations which can play an important role in establishing Schottky barriers at metal/polymer interfaces. In the device model, the region of the polymer near each contact is assumed to be in quasiequilibrium with that contact. The charge density as a function of position is found from the electrostatic potential and equilibrium statistics. Poisson's equation is integrated to determine the electrostatic potential. We find that a large charge density is transferred into the polymer if the chemical potential of a contact is higher than the negative bipolaron formation energy per particle or lower than the positive bipolaron formation energy per particle. The transferred charge pins the Fermi level and establishes the effective Schottky barrier. If the contact chemical potential is between the formation energy per particle of the two types of charged bipolarons, there is little charge transfer into the polymer and the Fermi level is not pinned. The electric field in the device is found for different contacts and bias conditions. Capacitance as a function of voltage is calculated for various trap binding energies and densities. The calculated results are used to interpret recent measurements on PLEDs. © 1995 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.359886
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
    Volltext
  • 4
    Digitale Medien
    Digitale Medien
    Chemical potential pinning due to equilibrium electron transfer at metal/C60-doped polymer interfaces (1997)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 81 (1997), S. 3227-3231 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We report electroabsorption measurements of the built-in electrostatic potential in metal/C60-doped polymer/metal structures to investigate chemical potential pinning due to equilibrium electron transfer from a metal contact to the electron acceptor energy level of C60 molecules in the polymer film. The built-in potentials of a series of structures employing thin films of both undoped and C60-doped poly[2-methoxy, 5-(2′-ethyl-hexyloxy)-1,4-phenylene vinylene] (MEH-PPV) were measured. For undoped MEH-PPV, which has an energy gap of about 2.4 eV, the maximum built-in potential is about 2.1 eV, whereas for C60-doped MEH-PPV the maximum built-in potential decreases to 1.5 eV. Electron transfer to the C60 molecules close to the metal interface pins the chemical potential of the metal contact near the electron acceptor energy level of C60 and decreases the built-in potential of the structure. From the systematic dependence of the built-in potential on the metal work function we find that the electron acceptor energy level of C60 in MEH-PPV is about 1.7 eV above the hole polaron energy level of MEH-PPV. © 1997 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.364154
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
    Volltext
  • 5
    Digitale Medien
    Digitale Medien
    Vacuum-UV fluorescence spectroscopy of SiF4 in the range 10–30 eV (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 107 (1997), S. 720-729 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: The vacuum-UV and visible spectroscopy of SiF4 using fluorescence excitation and dispersed emission techniques is reported. The fluorescence excitation spectrum has been recorded following excitation with synchrotron radiation from the BESSY 1, Berlin source in the energy range 10–30 eV with an average resolution of ∼0.05 eV. By comparison with vacuum-UV absorption and electron energy loss spectra, all the peaks in the Rydberg spectra that photodissociate to a fluorescing state of a fragment have been assigned. Dispersed emission spectra have been recorded at the energies of all the peaks in the excitation spectra. Four different decay channels are observed: (a) SiF3 fluorescence in the range 380–650 nm for photon energies around 13.0 eV, (b) SiF2 a˜ 3B1–X˜ 1A1 phosphorescence in the range 360–440 nm for photon energies in the range 15.2–18.0 eV, (c) SiF2 A˜ 1B1–X˜ 1A1 fluorescence in the range 210–270 nm for photon energies in the range 17.0–20.0 eV, and (d) emission from the D˜ 2A1 state of SiF4+ predominantly in the range 280–350 nm for photon energies greater than 21.5 eV. These assignments are confirmed by action spectra in which the excitation energy of the vacuum-UV radiation is scanned with detection at a specific (dispersed) wavelength. Using the single-bunch mode of the synchrotron, lifetimes of all the emitting states have been measured. The lifetimes of the unassigned emitting state in SiF3, the A˜ 1B1 state of SiF2, and the D˜ 2A1 state of SiF4+ are 3.9±0.7, 11.2±1.5, and 9.16±0.02 ns, respectively. This is the first measurement of the lifetimes of these excited states in SiF3 and SiF2. The decay from the a˜ 3B1 state of SiF2 has a fast component of 2.6±0.4 ns. We conclude that the lifetime of the a˜ 3B1 state of SiF2 is either as low as 2.6 ns or too high (τ〉∼200 ns) to measure with the timing profile of the single-bunch mode of BESSY 1. If the latter interpretation is correct, as seems likely for a spin-forbidden phosphorescence to the 1A1 ground state, the 2.6 ns component could be the lifetime of intersystem crossing from higher vibrational levels of the a˜ 3B1 state of SiF2 into its ground state. © 1997 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.474437
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
    Volltext
  • 6
    Digitale Medien
    Digitale Medien
    Theoretical study of the O-H stretching band in 3-hydroxy-2-methyl-4-pyrone (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 108 (1998), S. 9685-9693 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: The infrared spectrum of 3-hydroxy-2-methyl-4-pyrone reveals an O-H stretching frequency roughly 200 cm−1 lower than that of a typical alcohol group. The frequency lowering results from intramolecular hydrogen bonding between the alcohol and ketone groups. In this work, the stretching and bending vibrations of the O-H group in 3-hydroxy-2-methyl-4-pyrone are studied with a theoretical methodology more rigorous than the conventional harmonic approximation. A two-dimensional potential energy surface in internal coordinates corresponding to different hydrogen positions in the plane of the molecule is calculated with the use of the second order Møller-Plesset perturbation theory. To include all possible variations in kinetic energy in a large amplitude vibrational mode, g-matrix elements with variable values are employed. The analytical expression for the Hamiltonian matrix elements of the two-dimensional vibrational problem in a basis of shifted Gaussian functions is derived. Expectation values for the O-H stretch nuclear states are variationally determined with the use of shifted Gaussian functions as the basis set. The results of the calculations are compared with the recent matrix-isolation infrared (IR) spectroscopic results. The calculated transition frequency corresponding to the in-plane O-H stretching is found to be in good agreement with the experimental value. © 1998 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.476444
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
    Volltext
  • 7
    Digitale Medien
    Digitale Medien
    Effect of maternal weight on maternal serum ∞-fetoprotein (1982)
    Oxford, UK : Blackwell Publishing Ltd
    BJOG 89 (1982), S. 0 
    Details
    ISSN: 1471-0528
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Medizin
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1111/j.1471-0528.1982.tb04646.x
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
    Volltext
  • 8
    Digitale Medien
    Digitale Medien
    Limits of force microscopy (1995)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 66 (1995), S. 3191-3195 
    Details
    ISSN: 1089-7623
    Quelle: AIP Digital Archive
    Thema: Physik , Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: The atomic force microscope (AFM) is calculated to have quantum limited sensitivity using common optical detection techniques. Under typical ambient operating conditions, the AFM is shown to have an energy resolution better than 10−24 J, considerably weaker than the energy of 10−21 J/molecule for the weakest chemical bonds. For operation in vacuum, periodic forces of 10−15 N are detectable at room temperature. At 4.2 K it is possible to resolve single bursts of energy of 10−25 J. The AFM is shown to have many features in common with a resonant-bar gravitational wave antenna. © 1995 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1145550
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
    Volltext
  • 9
    Digitale Medien
    Digitale Medien
    The flexible x-ray imager (1996)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 67 (1996), S. 485-488 
    Details
    ISSN: 1089-7623
    Quelle: AIP Digital Archive
    Thema: Physik , Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: A new gated x-ray framing camera has been developed at the Lawrence Livermore National Laboratory for use at the Nova laser facility. This diagnostic, the flexible x-ray imager, has been designed as a modular unit that can be rapidly reconfigured to change the spectral response, magnification, sensitivity, and spatial and temporal resolutions of the instrument. The electrical gate pulse width may be varied from 200 ps to 2 ns depending upon whether the experimental emphasis is on temporal resolution or sensitivity. The long integration times are particularly useful in experiments where motional blurring occurs over even longer time scales. A detailed description of the instrument and its varied uses is presented. © 1996 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1146616
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
    Volltext
  • 10
    Digitale Medien
    Digitale Medien
    Device physics of single layer organic light-emitting diodes (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 86 (1999), S. 5767-5774 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We present experimental and device model results for electron only, hole only, and bipolar organic light-emitting diodes fabricated using a soluble poly (p-phenylene vinylene) based polymer. Current–voltage (I–V) characteristics were measured for a series of electron only devices in which the polymer thickness was varied. The I–V curves were described using a device model from which the electron mobility parameters were extracted. Similarly, the hole mobility parameters were extracted using a device model description of I–V characteristics for a series of hole only devices where the barrier to hole injection was varied by appropriate choices of hole injecting electrode. The electron and hole mobilities extracted from the single carrier devices are then used, without additional adjustable parameters, to describe the measured current–voltage characteristics of a series of bipolar devices where both the device thickness and contacts were varied. The model successfully describes the I–V characteristics of single carrier and bipolar devices as a function of polymer thickness and for structures that are contact limited, space charge limited, and for cases in between. We find qualitative agreement between the device model and measured external luminance for a thickness series of devices. We investigate the sensitivity of the device model calculations to the magnitude of the bimolecular recombination rate prefactor. © 1999 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.371591
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
    Volltext
Schließen ⊗
Diese Webseite nutzt Cookies und das Analyse-Tool Matomo. Weitere Informationen finden Sie hier...